The approval for the Northern Ireland section of the multi-million-pound project means work can begin on it later this year.
“This is a welcome decision and will help create a vital piece of infrastructure for Northern Ireland,” said Ms Armstrong.
“The interconnector is crucial to ongoing energy security, diversification and keeping costs as low as possible for domestic consumers.
“Energy infrastructure is a clear demonstration of practical north-south co-operation. We must remain vigilant against a hard or no deal Brexit putting that in real jeopardy.”